Most commercially-available electromagnetic shutters are driven by linear solenoids. While readily available and inexpensive, they are very inefficient shutter actuators. Inherently non-linear, they provide much-reduced force at the beginning of pull-in (just when the shutter requires maximum force to achieve high acceleration and short actuation time). They provide very short stroke, typically requiring troublesome lever mechanisms to match the longer stroke required by the shutter drive mechanism. Furthermore, the short stroke often requires tight manufacturing tolerance and/or custom alignment of solenoid to drive linkage. At smallest sizes, solenoids provide very poor power efficiency for given output force/stroke.
Rotary solenoids are sometimes used for shutter drive. And, while these sometimes contain non-linear helical ramps to smooth out the force/distance curve, they still have disadvantages in cost, energy efficiency, and size.
DC motor actuators have occasionally been used. While they offer more linear force/torque output and better power efficiency, they still have several disadvantages. Their size/shape configuration is not well matched to the low-profile donut-shaped space envelope requirements of an optical shutter. Size trade-offs (tiny motors) reduce power efficiency. Power coupling drives are sometimes costly and/or inefficient. Motor inertia slows the start/stop response. And motor brushes add reliability and debris concerns for this short-stroke start/stop application.
Some proprietary electromagnetic shutter drives (i.e., Kodak) use magnets and coils to drive a shutter. However, these all include an iron core electromagnet. These have the disadvantage of higher inductance of the coil assembly. And most of these designs have magnet/pole cogging (requiring higher drive current just to overcome magnet/pole attraction before actuator motion takes place.)
Thus, there is a continuing need for new and improved shutter actuation mechanisms and technology. I have, therefore, developed a voice coil drive for optical shutters. The resultant voice coil shutter drive system, driven by Lorentz forces between electromagnet coil and permanent magnetic flux, allows a very energy efficient, cost efficient linear actuation mechanism for an optical shutter mechanism. In addition, it offers numerous other advantages over current technology:
First, a superior linear force curve (force is fairly constant for given drive current, regardless of actuator position), allowing a smooth, fast and efficient shutter drive.
Second, its coreless magnetic design allows driving at low currents (as it does not have to overcome magnetic cogging of typical motor designs).
Third, it can have low inertia moving mass, allowing efficient high-speed actuation.
Fourth, its simplicity and long-strong actuation allow simple, cost efficient manufacturing of shutter assemblies. Tight tolerances and custom fit-up are not required.
Fifth, my direct drive system offers good system reliability and efficient power transfer.
Sixth, the size/shape and configuration of my system can be well matched to fit within compact shutter space envelopes, even while allowing substantial magnet flux (and thus high energy efficiency).